An mmap'ed audio driver sounds pretty weird to me. Yes, you can
make use of it to reduce the kernel/user data transfer, but you
can do that the other way around. [...]
That's true only if the samples you're playing are already in a file.
(And even then, you could just do memory-to-memory copy if both things
are mapped.) In other cases, like xquake B-) and AudioFile, this is
not the case, and eliminating the copy time is actually a big win. One
of the AudioFile authors specifically asked me about this, in fact.